Electronic article surveillance (EAS) technology is a widely used method for preventing shoplifting from retail and other stores. EAS technology is used to identify articles as they pass through a gated area in a store. In practice, an EAS tag or label is attached to an article. The tag is deactivated so that it will not flag an alarm. If the tag is a hard, reusable tag, a detacher is used to remove it when a customer purchases the tagged item. If the tag is disposable, it can be deactivated by swiping the article over a pad or with a handheld scanner.
Radio frequency identification (RFID) systems are used world-wide. A tag or label attached to a product responds to a specific frequency emitted by a transmitter antenna. The response from the RFID tag is picked up by a receiver antenna. This processes the tag response signal and triggers an alarm when specific criteria are matched. RFID EAS tags are essentially an LC circuit having a resonance peak frequency between about 2 MHz and about 10 MHz. The most popular frequency is 8.2 MHz. The 8.2 MHz tag is deactivated by subjecting the tag to a strong magnetic field at the resonant frequency to induce voltage exceeding the breakdown voltage and detune the circuit by partially destroying the capacitor.
Currently, high frequency (HF) EAS tags require a parallel plate capacitor to be made to resonate the coil at 8.2 MHz. In addition, the coil must have a defined breakdown voltage to allow the device to be deactivated by exposing it to high field strength.